Turbocharger actuator

ABSTRACT

A turbocharger actuator and a method of calibrating the actuator is particularly applicable to a variable nozzle turbocharger (VNT). The actuator comprises an actuator housing having a diaphragm connected across it, a piston, a compression spring arranged to be generally centred in the actuator housing and to bias the piston and keep the diaphragm for calibrating a turbocharger. The actuator housing may be connected to a bracket using three rivets and the diaphragm may crimped to connect it to the actuator housing coated with elastomer bead to improve and control the crimping process. The shape of the piston is modified to reduce the overall length of the actuator. The bracket for attaching the actuator assembly to the variable nozzle turbocharger housing comprises a first planar portion having a plurality of rivet holes formed therein for connection to the actuator assembly, and at least one, preferably two, second portion(s) extending generally perpendicular to the first portion and having an elongate hole formed therein to receive a bolt to attach the bracket to the turbocharger housing, the elongate hole allowing a sliding movement of the actuator assembly relative to the turbocharger housing. The calibration method comprises applying a predetermined vacuum to the actuator to allow the actuator to take a calibrated position determined by gravity whilst keeping the pin crank in contact with the flow screw of the turbocharger and tightening the or each bolt, at a predetermined torque, to tighten the attachment of the actuator assembly to turbine housing. The actuator calibration is controlled as normal and if it is not correct hen the process is repeated using a different predetermined vacuum value.

The present invention relates to a turbocharger actuator and a method ofcalibrating the actuator. It is particularly applicable to a variablenozzle turbocharger (VNT).

Turbochargers are used extensively in modem diesel engines to improvefuel economy and minimize noxious emissions. Traditionally aturbocharger comprises a turbine wheel in a chamber within a turbinehousing, a compressor wheel and housing, and a central cast bearinghousing for journaling a shaft which connects the compressor and turbinewheels. The turbine wheel rotates when driven by exhaust gasses from aninternal combustion engine and causes the compressor wheel to rotate andcompress air for delivery to the engine at a rate that is greater thanthe rate the engine can naturally aspirate. The turbocharger pressureoutput is a function of component efficiencies, mass flow through theturbine and compressor and the pressure drop across the turbine.

A VNT typically comprises a substantially cylindrical piston receivedwithin the turbine housing concentrically aligned with the rotationalaxis of the turbine. The piston is longitudinally movable to set thearea of the inlet nozzle to the turbine from the volute so as tomodulate the performance of the turbocharger for different operatingconditions. The piston is moved by an actuator which is usuallypneumatically operated and which is attached to the turbine housing by abracket. It is necessary to calibrate the actuator when it is fitted.

Traditionally a VNT is calibrated using two fixed end points with amanually adjustable connecting rod and end. The rod and end is held inplace by a locknut and the actuator assembly is held by two bolts andnuts. Conventional parts of a VNT are difficult to fit and adjust inconfined spaces, and the manual calibration process reduces assemblyline productivity, increases costs and tends to be relativelyunreliable.

There is a need for a more robust actuator design and calibrationprocess to enable automatic calibration and compact turbochargerinstallations, as well as to increase assembly line productivity andreduce the cost of an actuator. It is also desirable to make thecalibration process calibration process to enable automatic calibrationand compact turbocharger installations, as well as to increase assemblyline productivity and reduce the cost of an actuator. It is alsodesirable to make the calibration process more reliable and reduce thewarranty returns, for example for loss of calibration.

According to one aspect of the present invention there is provided anactuator for a variable nozzle turbocharger, comprising: an actuatorhousing; a piston; a diaphragm, connected across the actuator housing;at least one compression spring arranged to be generally centred in theactuator housing and to bias the piston; a spaded rod, connected to thepiston, for calibrating a turbocharger, and a bracket comprising a firstplanar portion for fixedly connecting to the actuator assembly, and atleast one second portion extending generally perpendicular to the firstportion and having an elongate hole formed therein to receive means forattaching the bracket to the turbocharger housing, the elongate holeallowing a sliding movement of the actuator assembly relative to theturbocharger housing.

Preferably the actuator housing is connected to the bracket using atleast one, and preferably three, rivets. The diaphragm may be crimped toconnect it to the actuator housing and it may be coated with elastomerbead to improve and control the crimping process.

Advantageously the shape of the piston in the actuator is modified toreduce the overall length of the actuator.

According to a preferred embodiment the bracket comprises a thirdportion extending perpendicular to the first portion and being generallyparallel to the second portion and the third portion having an elongatehole formed therein to receive a bolt to attach the bracket to theturbocharger housing, the elongate hole allowing a sliding movement ofthe actuator assembly relative to the turbocharger housing.

Preferably the elongate holes allow around 4 mm of sliding movement(+/−2 mm).

According to a second aspect of the present invention there is provideda method of calibrating a variable nozzle turbocharger comprising thesteps of:

-   -   a) using an actuator assembly which has a spaded rod;    -   b) using at least one bolt to attach the actuator assembly to an        end housing (of either a compressor or a turbine) which has a        pin crank so that the spaded rod is adjacent to the pin crank;    -   c) applying a predetermined vacuum to the actuator, through an        actuator port to allow the actuator to take a calibrated        position determined by gravity;    -   d) keeping the pin crank in contact with the flow screw of the        turbocharger;    -   e) tightening the or each bolt, at a predetermined torque, to        tighten the attachment of the actuator assembly to the end        housing;    -   f) controlling the actuator calibration in accordance with        predetermined process instructions;    -   g) determining whether the calibration process is correct and if        it is not correct then repeating the process from step c) using        a different predetermined vacuum value.

According to a preferred embodiment of the second aspect of theinvention the method is conducted using the actuator assembly of thefirst aspect.

The compact design of the new actuator and the novel calibrationprocedure enable application of a VNT in confined spaces whereconventional parts would be difficult or impossible to fit and adjust.In addition, automation of the calibration process is enabled, providingincreased production line capacity.

For a better understanding of the present invention, and to show how thesame may be carried into effect, reference will now be made to theaccompanying drawings, in which:

FIG. 1 is a cross-section of an actuator for a variable nozzleturbocharger according to one embodiment of the invention;

FIG. 1A is a cross section of an actuator for a variable nozzleturbocharger showing a design according to the prior art;

FIG. 2 is a perspective view of part of the known actuator of FIG. 1A.

FIG. 3 is a perspective view of part of the actuator of FIG. 1,according to one embodiment of the invention;

FIG. 4 is a side view of a known bracket for fixing the known actuatorof FIG. 2 to a variable nozzle turbocharger;

FIG. 5 is a perspective view of one embodiment of a new bracket forfixing the new actuator of FIG. 3 to a variable nozzle turbocharger.

FIG. 6 is a side elevation view of the known actuator of FIG. 2 attachedby the known bracket of FIG. 4 to a variable nozzle turbocharger.

FIG. 7 is a side elevation view of the new actuator of FIG. 3 attachedby the new bracket of FIG. 5 to a variable nozzle turbocharger.

FIG. 8 is a cross-sectional view of the new actuator of FIG. 3illustrating the new calibration method.

FIG. 9 is a perspective view of the new actuator and another embodimentof a new bracket.

In FIG. 1A the known actuator assembly comprises a diaphragm 1A crimpedat 2A into the side wall of an actuator assembly 3A. A spring 4A holdsthe diaphragm 1A taut and controls the position of actuator piston 8A.Two sets of bolts and nuts, of which one is shown at 9A, are used tohold the bottom wall of the actuator assembly 3A to a bracket assembly18A which in turn will be connected to a turbine housing (not shown). Acalibration rod 5A extends through a gimball 11A and is held in place bya locknut 6A and is fixed at one end to the actuator piston 8A. A heatshield 12A protects the actuator. A stud 13A passes through the bottomwall of the actuator assembly 3A and a double plate 17A.

The rod 5A has an adjustable rod end 15A and a bolt hole 21A for fixingto either the compressor or the turbine housing of the turbocharger.

By contrast, in FIG. 1, a modified actuator assembly is shown accordingto the invention. The two bolts and nuts 9A are replaced by threerivets, of which two are shown at 7, and the actuator assembly 3combines the functions of actuator assembly and bracket assembly. Therod end 5A and the locknut 6A are replaced by a rod 5 with spaded(flattened) end portion 15 shown in profile in FIG. 1. This new shapefor the rod end assists the calibration process as will be describedlater. A spaded rod is a design known for use in wastegatedturbochargers but has not hitherto been used in variable nozzletechnology because the calibration process is not the same. Specificallythe spaded rod 5 has a flat portion at one end formed by cold forgingwith a hole to be connected to the pin crank of the turbocharger. Acompression spring 4, in the inventive modification, is centered in theactuator assembly 3 and this reduces the hysteresis, ie theinaccuracies, particularly in calibration, due to the imperfections inthe spring 4 itself. The diaphragm 1 is crimped into the side wall 3 ofthe actuator assembly at 2 and this is improved in the invention by acrimping control achieved by the addition of elastomer bead 46 on thediaphragm 1. Elastomer bead can accept more variation in compressionduring the crimping process used to close the actuator than a flat shapewhich is traditionally used by the applicant, or a metal to metalcontact as traditionally used by other people in the field.

The elastomer bead 46 also improves the seal capability. The convolutionof the diaphragm 1 has a reduced width to reduce the diaphragm stressand the overall diameter of the actuator.

In addition, the piston 8 has a shape modification which reduces theoverall length of the actuator assembly, as can be seen by comparingFIG. 1 with FIG. 1A. The new bracket is shown at 18 and the gimble isshown unchanged at 11.

The piston 8 must withstand 1.7NM torque, with respect to the rod end 5,without relative motion. The engineering requirements are 0.15 SCCM maxunder 1.5 bars and a pull test of 100 Kg.

FIG. 2 is a perspective view from below of a traditional design of aturbocharger actuator assembly, ie a view from below of the assembly inthe left hand side of FIG. 1. The heat shield 12A is shown part cut-awayand the side wall of the actuator assembly 3A is attached to the bracketassembly 18A by two nuts 9A. The rod end 15A is held in place by alocknut 6A and is adjustable. Thus, traditionally, calibration iseffected by two fixed end points with a manually adjustable connectingrod and end.

By contrast, the inventive actuator assembly of FIG. 3 has a side wallof actuator 3 held to the bracket assembly 18 by the three rivets 7 andno locknut is needed because the rod 5 is spaded at the end 15 and offixed length. Thus, the actuator end-point is allowed to move, and therod and the second end point are fixed. When a calibrated vacuum isapplied to the actuator, the actuator body is moved towards the fixedend point until forces are equalized. The actuator 3 is then in thecalibrated position and is fixed to the compressor or the turbinehousing by accessible bolts and bracket.

The traditional shape of the bracket 18A is shown in detail in the plandrawing of FIG. 4 which also shows the positions of two bolts 10A whichhold the bracket 18A to a traditional turbocharger body. Such anarrangement is shown in the side view of FIG. 6 where a traditionalturbocharger 20 is attached to a traditional actuator 30A by thetraditional bracket 18A which is attached to the actuator by two boltsand nuts 19A. The traditional adjustable rod end 15A is shown.

In FIG. 5 the shape of the new bracket 18 is shown with a generallytriangular plate section 31 having three rivet holes 32, and two bentsections 33 and 34 having elongate bolt holes 35 and 36 respectively. Acentral hole 37 accommodates the fixed length new shaped rod 5 with end15. As shown in the side view of FIG. 7, the new bracket 18 is used toconnect the new actuator body 30 to a turbocharger 20. The plate section31 is riveted to the actuator housing by three rivets 7 and the bentportions 33 and 34 are connected to the turbocharger 20 either to theturbine housing or the compressor housing by two bolts 38 through theslot shaped holes 35 and 36. The elongate shape of the holes 35, 36allows adjustment during calibration and obviates the need for the rodend 15 on the actuator 30 to be adjustable.

FIG. 6 shows a traditional actuator assembly 30A, such as that shown inFIG. 2 and of FIG. 1A, attached to a turbine housing 20 by means of thebracket of FIG. 4 by means of bolts and nuts 19A. The rod end 15A isshown.

FIG. 7 shows a new actuator assembly 30, such as that shown in FIG. 3and FIG. 1, attached to a turbine housing 20 by means of the bracket ofFIG. 5. The attachment is by rivets 7 through the first portion of thebracket 31 and bolts 38 through at least the second portion of thebracket allowing a sliding movement of the actuator 30 relative to theturbine housing 20 as shown by the arrow 39.

FIG. 8 illustrates the new calibration method and comprises a crosssectional view of the inventive actuator.

The new calibration process comprises attaching the actuator 30 andbracket assembly 18 onto the turbocharger 20 in a vertical position withthe actuator head down and the spaded rod 5 adjacent to the pin crank40. Vacuum is applied to the actuator port 42. The actuator willnaturally take its calibrated position under the influence of gravity.The pin crank 40 is put in contact with the VNT flow screw as shown bythe arrow 41. The attachment bolts 38 (FIG. 7) are then tightened at therequired torque and the actuator calibration is controlled according tonormal process instructions. If the actuator calibration is not correct,then the bolts 38 are unscrewed and the process is repeated from step 2with a modified vacuum value.

FIG. 9 shows the new actuator 3 assembled to the bracket 18 and showsthe rod 5 and spaded rod end 15 together with the rivet holes 32 and theslot holes 35, 36 in the bent portions 33, 34 respectively. Theslot-type holes 35, 36 accept a sliding movement The heat shield 12 isalso shown.

1. An actuator for a variable nozzle turbocharger, comprising: anactuator housing; a piston; a diaphragm, connected across the actuatorhousing; at least one compression spring arranged to be generallycentred in the actuator housing and to bias the piston; a spaded rod,connected to the piston, for calibrating a turbocharger, and a bracketcomprising a first planar portion for fixedly connecting to the actuatorassembly, and at least one second portion extending generallyperpendicular to the first portion and having an elongate hole formedtherein to receive means for attaching the bracket to the turbochargerhousing, the elongate hole allowing a sliding movement of the actuatorassembly relative to the turbocharger housing.
 2. An actuator accordingto claim 1 wherein the bracket further comprises a third portionextending perpendicular to the first portion and being generallyparallel to the second portion and the third portion having an elongatehole formed therein to receive a bolt to attach the bracket to theturbocharger housing, the elongate hole allowing a sliding movement ofthe actuator assembly relative to the turbocharger housing.
 3. Anactuator according to claim 1 or claim 2 wherein the or each elongatehole allow(s) approximately 4 mm of sliding movement.
 4. An actuatoraccording to any one of the preceding claims wherein the actuatorhousing is connected to the bracket using at least one rivet.
 5. Anactuator according to claim 4 wherein the actuator housing is connectedto the bracket using three rivets.
 6. An actuator according to any oneof the preceding claims wherein the diaphragm is crimped to connect itto the actuator housing.
 7. An actuator according to any one of thepreceding claims wherein the diaphragm is coated with elastomer bead. 8.A turbocharger comprising a turbine, a compressor and an actuator, forcontrolling movement of the piston to control the air inlet to theturbine or the compressor, wherein the actuator is made accordingly toany one of the preceding claims.
 9. A method of calibrating a variablenozzle turbocharger comprising the steps of: a) using an actuatorassembly which has a spaded rod; b) using at least one bolt to attachthe actuator assembly to an end housing of a turbocharger which has apin crank so that the spaded rod is adjacent to the pin crank; c)applying a predetermined vacuum to the actuator, through an actuatorport to allow the actuator to take a calibrated position determined bygravity; d) keeping the pin crank in contact with the flow screw of theturbocharger; e) tightening the or each bolt, at a predetermined torque,to tighten the attachment of the actuator assembly to an end housing; f)controlling the actuator calibration in accordance with predeterminedprocess instructions; g) determining whether the calibration process iscorrect and if it is not correct then repeating the process from stepc)using a different predetermined vacuum value.
 10. A method accordingto claim 9 when conducted using the actuator of any one of the precedingclaims.
 11. An actuator according to any one of claims 1 to 7 when usedin the method of claim 9 or claim 10.